Spectacles can distort the visual world in a number of ways. Progressive and multifocal lenses impose substantial geometric distortion on the peripheral vision as a price for a wide, distortion-free clear view in the center (Selenow et al., 2002). In progressive addition lenses (PAL) the mean curvature of the optical surface varies gradually along a region called intermediate vision corridor to provide variable optical power for the eye (Sheedy et al., 1987). Around this area the PAL unavoidably introduces some undesired optical effects like blurring, non-uniform magnification, that is, distortion, and image displacement (Barbero and Portilla, 2016). These effects cause impairments in visual perception, including space (Guilloux et al., 2012) and depth (Faubert, 2002). Image distortions can also alter the performance of subjects in visual search tasks (Vu et al., 2008, Cho et al., 2012). This could be due to subjective changes in perceived quality of images, or objective changes in saliency of objects which may render them less conspicuous to the eye.
Despite the widely shared belief in the general public that ‘we see everything around us’, only a small fraction of the information registered by the visual system reaches levels of processing that mediate perception and directly influence behavior (Itti and Koch, 2000). Attention is the key to this process that turns looking into seeing by a selective mechanism (Carrasco, 2011). This selection process can be feature-based, space-based or object-based (Logan, 1996) and essentially optimizes the use of the system's limited resources by enhancing the representations of the relevant locations or features of the visual environment against less relevant items.
The ability to orient vision rapidly towards salient objects in cluttered scenes has evolutionary significance because it allows the animal to detect quickly prey and predators in the visual world. In the modern human era, we are not concerned much about predators, but our daily life and social interactions rely heavily on a rapid and reliable visual processing. Impairment of a fast pre-attentive mechanism for visual search has fatal implications in situations like driving, where rapid reaction to visual stimuli is important. If a stimulus is sufficiently salient, it will pop out of a visual scene. A salient stimulus for a driver can be other moving vehicles, pedestrians running onto the road, or traffic signs and warnings. The speed of this saliency-based form of attention is on the order of 25 to 50 milliseconds per item (Itti and Koch, 2001) which is sufficiently fast for tasks like driving. Volitional deployment of attention is slower—200 milliseconds or—more but can operate in parallel.
However, in the current optical system configuration method, the influence of the optical system on the attentional performance is not considered.